Monel 400 (UNS N04400)
The nickel-copper alloy that shrugs off seawater, brine and hydrofluoric acid — the classic marine and chemical fastener material, non-sparking and tough to cryogenic temperatures.
What Monel 400 is.
Monel 400 is a nickel-copper alloy with at least 63 percent nickel and 28 to 34 percent copper. It cannot be hardened by heat treatment, so its strength comes from cold work; as a fastener it delivers 80 ksi tensile in sizes to ¾ inch and 70 ksi above that under ASTM F468. It is one of the few metals that resists flowing seawater, brine, hydrofluoric acid and caustic alkalis at the same time.
We machine Monel 400 studs, bolts, nuts and components from certified B164 bar and certify them to F468 and F467, with a 3.1 report on every lot.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Nickel | Ni | 63.0 | 70.0 |
| Copper | Cu | 28.0 | 34.0 |
| Iron | Fe | — | 2.5 |
| Manganese | Mn | — | 2.0 |
| Carbon | C | — | 0.3 |
| Silicon | Si | — | 0.5 |
| Sulfur | S | — | 0.024 |
Values per ASTM B164-03(2019) Table 3 and ASTM F468-23 Table 1 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. Nickel is determined by difference; F468 lists copper as the balance.
Mechanical properties.
| Nominal diameter (in.) | Hardness | Full-size tensile (ksi) | Full-size yield, min (ksi) | Machined tensile, min (ksi) | Machined yield, min (ksi) | Elongation in 4D, min (%) |
|---|---|---|---|---|---|---|
| 0.250 to 0.750 | 75 HRB – 25 HRC | 80–130 | 40 | 80 | 40 | 20 |
| 0.875 to 1.500 | 60 HRB – 25 HRC | 70–130 | 30 | 70 | 30 | 20 |
| 0.875 to 1.500 (F468U4, high strength) | 75 HRB – 25 HRC | 80–130 | 40 | 80 | 40 | 20 |
Values per ASTM F468-23 Table 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. Full-size tensile range and yield; machined-specimen minimums in the last three columns.
| Nut style | Hardness, min | Proof stress, min (ksi) |
|---|---|---|
| Hex and hex flange | 75 HRB | 80 |
| Heavy hex, large hex flange and thick | 75 HRB | 86 |
Values per ASTM F467-24 Table 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
| Condition and size | Tensile strength, min (ksi) | Yield strength 0.2%, min (ksi) | Elongation, min (%) |
|---|---|---|---|
| Cold worked, stress relieved — rounds ½ to 3½ in. | 87 | 60 | 20 |
| Cold worked, stress relieved — rounds under ½ in. | 84 | 50 | 10 |
| Hot worked, as worked or stress relieved — to 12 in. | 80 | 40 | 30 |
| Annealed — all sizes | 70 | 25 | 35 |
Values per ASTM B164-03(2019) Table 1 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Specifications that apply.
How Monel 400 ships from Houston.
- Studs, hex bolts and cap screws to F468
- Hex and heavy hex nuts to F467
- Socket head cap and set screws
- Pump, valve and marine components machined to print
- Certified B164 bar, cold drawn or hot finished
Monel 400 fasteners we make.
Every item is manufactured to your drawing or standard in Monel 400, imperial or metric, with an EN 10204 3.1 certificate.
What is Monel 400?
Monel 400 was one of the first commercial nickel alloys, produced from a naturally nickel-copper ore. It is a single-phase solid solution, so it is not heat treatable; strength is set by the amount of cold work. Its combination of corrosion resistance in reducing environments, seawater and hydrofluoric acid, together with toughness from cryogenic temperatures to about 1000 °F, keeps it in continuous use for marine and chemical fasteners a century after its introduction.
Where it beats stainless
Stainless steels depend on a passive oxide film that chlorides attack. Monel 400 does not, so it resists pitting and crevice corrosion in stagnant seawater and brine where 316 fails, and it is one of the very few engineering alloys usable in hydrofluoric acid. It is not suited to oxidising acids such as nitric, or to sulfur-bearing gases above about 700 °F.
Fastener grades and nuts
ASTM F468 covers Monel 400 bolts as Ni 400 (marking F468U), with 80 ksi tensile in sizes to ¾ inch and 70 ksi above, or, for ⅞ to 1½ inch, the F468U4 marking that holds 80 ksi and 40 ksi yield in the larger sizes. Nuts are Ni 400 to F467 (F467U) with an 80 ksi proof stress. Monel-on-Monel threads gall, so use an anti-seize.
Testing, certification and marking
- Tensile and hardness tested per lot on the finished product
- Grade or alloy marking F468U on bolts and F467U on nuts and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
Monel K-500 (UNS N05500)
Monel 400 corrosion resistance with more than twice the strength — 130 ksi tensile, 90 ksi yield and 24 to 37 HRC — for pump shafts, subsea fasteners and oil-tool components.
ASTM B637 bar · AMS 5662 / 5663 · API 6A CRAInconel 718 (UNS N07718)
The premier high-strength nickel superalloy — 185 ksi tensile and 150 ksi yield from cryogenic temperatures to 1200 °F, with corrosion and sour-gas resistance to match.
ASTM A193 / ASME SA-193ASTM A193 Grade B8M Class 1 (316 Stainless)
316 stainless bolting with molybdenum for chloride and pitting resistance — offshore, marine, chemical and coastal plant fasteners.